Pasteurization of foods is a thermal process to achieve a partial sterilization with significant (e.g. 5-log) reduction of food spoilage organisms and pathogens like Clostridium botulinum, Salmonella spp., E. coli, Usteria spp., Campylobacter spp., Staphylococcus spp., etc. The microorganism of greatest concern is Clostridium botulinum, a gas forming anaerobe that produces a lethal exotoxin, but other spoilage organisms present need to be inactivated. The thermal process is designed to destroy or inactivate these organisms. Certain bacteria may survive the process, but their levels are greatly reduced, so that the product is rendered safe, although not necessarily sterile. The pasteurization process needs to be carried out in a way which is controlled and highly consistent and which does not damage or destroy either the container or the food.
Pasteurization process has been broadly utilized in many food productions for ready to eat products such like refrigerated cooked meat products, infant formula, Jello, tomato sauces, juices, etc. Usually, pasteurization is carried out before packaging and prior to sealing into structurally strong, heat-resistant containers like bags, bottles, jars, cartons, or cans. By refrigeration, low moisture content, or low pH in conjunction with either hot filling or aseptic packaging, those packaged foods can achieve food safety requirement along with a reasonable shelf life. Post packaging pasteurization has also been utilized for processing shelf stable low pH and high moisture food without either hot filling or aseptic packaging; however, those products are usually packaged in rigid containers like metal cans or glass jars in order to withstand pressure expansion during the process.
Plastic food containers are popular, as they can be recycled, they require less energy to manufacture than metal containers, they are suitable for use in a microwave, and they allow for see-through packaging and/or packaging with customized shapes, coloring and labeling. Plastic containers may be less heat- or pressure-resistant than glass or metal containers; especially, pasteurization of food in a sealed plastic container presents particular challenges, because pressure expansion upon heating can easily distort or rupture the package. Thus where plastic containers are used, the food is usually pasteurized by heating, followed by hot filling or aseptic packaging of the plastic cup, tray or flexible pouch. Flexible vacuum-sealed pouches may in some cases be pasteurized post-filling, as they typically do not contain any significant headspace, so the only expansion is the expansion of the food, and they are flexible and relatively elastic, and so can tolerate some expansion of the food. Alternatively, clear plastic containers can be cold pasteurized with UV light. There is however still a significant need for a commercially practical system for pasteurizing food packaged inside a rigid or semi-rigid container, e.g. a plastic tray.